Localization of dopamine D1 and D2 receptors in the rat neostriatum: synaptic interaction with glutamate- and GABA-containing axonal terminals.

In order to determine the synaptic interactions between the glutamate- and GABA-containing axonal terminals and the two subpopulations of medium spiny neurons in the rat neostriatum, double immunocytochemistry was performed. Sections of perfuse-fixed rats were used. Immunoreactivity for dopamine D1 and D2 receptors was used as a marker for the two subpopulations of spiny neurons that give rise to the direct and indirect pathways, respectively. Receptor immunoreactivity was first revealed by preembedding immunostaining. Postembedding colloidal gold labeling was then performed to reveal immunoreactivity for glutamate or GABA. The results were analyzed at the electron microscopic level. Both the D1-immunoreactive, presumed striatonigral/entopeduncular neurons, and the D2-immunoreactive, presumed striatopallidal neurons, were found to receive qualitatively similar synaptic inputs from glutamate-immunoreactive terminals and GABA-immunoreactive terminals. The present results indicate that the different classes of spiny neurons are thus likely to be under a similar regime of excitatory and inhibitory control.